A 1923 piece by Wilhelm Lachnit titled 'Man and Woman in the Window." / Public Prosecutor Office Augsburg via epa

by John Bacon, USA TODAY

by John Bacon, USA TODAY

The German government has set up a website to provide detailed descriptions for hundreds of art treasures stolen by the Nazis during Hitler's reign and seized from a Munich apartment 21 months ago.

Almost 600 of 1,400 pieces, confiscated from German collector Cornelius Gurlitt, were stolen or bought for small sums from Jewish collectors who were forced to sell, German authorities said. Among the pieces are works by Henri Matisse and Pablo Picasso.

Heirs of the Jewish collectors have been pressing the German government for information since the German magazine Focus last week published news of the stash, valued at more than $1 billion. German Chancellor Angela Merkel's spokesman, Steffen Seibert, said this week that the government understood the demands of Jewish groups and art experts that descriptions of the pieces be quickly made public.

Works that appear to have been seized from Jews or others persecuted by the Nazis are being posted on the site lostart.de, although the website was struggling to function Tuesday. "There are simply too many people who want to look at the pictures and that's why we're facing technical problems," said Sabine Kramer from the Lost Art Internet Database.

Among the paintings listed now are Otto Dix's The Woman in the Theater Box, Otto Griebel's Child at the Table, and Max Liebermann's Riders on the Beach.

Two attorneys in Berlin had been searching for five years for the Liebermann, on behalf of the work's heirs. Attorney Jörg Rosbach told the German magazine Der Spiegel that he became enraged when he learned the painting had been seized -- and no one had been notified.

Rosbach called one of the heirs in New York. The next day, David Toren called back. "Our Liebermann was even shown in The New York Times," Toren said, "It used to hang in Uncle David's house, in the room in front of the winter garden."

The Wall Street Journal reported that German Foreign Ministry officials discussed the treasures with U.S. Embassy officials last week. The Journal, citing a person familiar with the talks, said the State Department urged Germany to publish the list of works, eliminate the country's 30-year statute of limitations on stolen art and establish a formal claims process for victims to recover their works.

The discovery of the art stash resulted from an ongoing tax probe of Gurlitt. Not all the pieces have been missing for decades - some were exhibited in New York and San Francisco in 1956, Frankfurt art expert Allgemeine Sonntagszeitung told The Guardian.

"We can well understand that especially Jewish organizations are asking many questions. They represent older people who were treated very badly," Seibert said.

A task force of six experts is being formed to expedite identification of the art and the rightful owners, Seibert said.

Gurlitt had reportedly been holed up in his apartment since news of the find broke last week, but The New York Times reported that Gurlitt was seen leaving his apartment Tuesday in a taxi bound for the airport -- no word on where he was headed.